Shade-Dwelling Corals of the Great Barrier Reef

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Abstract
Shade-dwelling corals were studied from 127 caves, tunnels, and overhangs from a variety of reefs within the Great Barrier Reef Province. Over 3000 coral colonies were recorded from these shaded habitats, and more than 150 spp., mostly hermatypic, were represented. Three groups of shade-dwelling corals are tentatively distinguished: generally skiophilous (shade-loving) corals, found both in deep water and in shallow but shaded conditions; preferrentially cavernicolous corals, growing mostly in shallow, shaded habitats; and shade-tolerant corals, common also in better illuminated parts of the reef, but tolerant of a wide range of conditions. Hermatypic shade-dwelling corals usually have thin, flattened growth forms and the coralla are generally small, suggesting that low light intensity is restricting both the shape and size of colonies. Apart from an abundance of ahermatypic corals on the ceilings of some cavities, particular faunal zoens were not detected in different sectors of cavities or at different irradiance levels. This lack of zonation is attributed principally to 2 factors. The coral fauna represents only a well-shaded but not obscure (dark) aspect of skiophilous communities. Ahermatypic corals were not found in conditions darker than those tolerated by some hermatypic species.